The invention generally relates to surgical devices and, more particularly, to surgical devices and methods for use in procedures performed on moving tissue.
Some forms of surgery involve ablation to kill tissue in an organ in order to achieve a therapeutic result. Ablation can be achieved by various techniques, including the application of radio frequency energy, lasers, cryogenic probes, and ultrasound. Thus, the term xe2x80x9cablation,xe2x80x9d as used herein refers to any of a variety of methods used to kill tissue within an organ. To be successful, ablation treatment may require considerable precision. The surgeon must target a particular region, and be careful not to cause unnecessary trauma to other areas of the patient""s body near the target area. Just as important, the surgeon must be confident that the procedure within the target area has been appropriately performed. For example, the surgeon may need to determine whether the tissue has been ablated to an appropriate degree. The surgery may be made more difficult if the target area is moving.
One such surgical procedure in which a surgeon may wish to ablate moving tissue is an operation to correct an abnormal heartbeat. To function efficiently, the heart atria must contract before the heart ventricles contract. As blood returns to the heart and enters the atria, blood also flows through the atrioventricular (AV) valves and partially fills the ventricles. Following an electrical excitation by the sinoatrial (SA) node, the atria contract in unison, expelling blood into the ventricles to complete ventricular filling. The ventricles then become excited and contract in unison. Ventricular contraction ejects the blood out of the heart. Blood ejected from the right ventricle enters the pulmonary arteries for oxygenation by the lungs, and blood ejected from the left ventricle enters the main aorta and is distributed to the rest of the body. If the timing of cardiac functions is impaired, such as by the atria not contracting in unison or by the ventricles contracting prematurely, then the operation of the heart is impaired.
The synchronization of heart functions is initiated by an excitation from the SA node, which is the heart""s natural pacemaker. The excitation propagates along an interatrial pathway, extending from the SA node in the right atrium to the left atrium. The excitation then spreads across gap junctions throughout the atria, causing the atria to contract in unison. The excitation further travels down an internodal pathway to the AV node, which transmits the excitation to the ventricles along the bundle of His and across the myocardium via the Purkinje fibers. In an aging heart, the atria may stretch, and the conduction paths by which the excitations travel may become lengthened. As a result, the excitations have a longer distance to travel, and this may affect the timing of the heart contractions and may create an arrhythmia. The term xe2x80x9carrhythmiaxe2x80x9d is used to describe any variation from normal rhythm and sequence of excitation of the heart.
One form of arrhythmia is atrial fibrillation. Atrial fibrillation is characterized by chaotic and asynchronized atrial cell contractions resulting in little or no effective blood pumping into the ventricle. Ventricular contractions are not synchronized with atrial contractions, and ventricular beats may come so frequently that the heart has little time to fill with blood between beats. Atrial fibrillation may occur if conduction blocks form within the tissue of the heart, causing the electrical excitations to degenerate into flurries of circular wavelets, or xe2x80x9creentry circuits,xe2x80x9d which interfere with atrial activity. Initiation or maintenance of atrial fibrillation may be facilitated if atria become enlarged. Atrial enlargement increases the time required for the electrical impulse to travel across the atria. This allows sufficient time for the cells that contracted initially to repolarize and allows the re-entry circuit to be maintained.
One surgical procedure for treating some forms of arrhythmia is to disrupt conduction paths in the heart tissue by severing the paths at selected regions of the atrial myocardium. Selective disruption of the conduction pathways permits impulses to propagate from the SA node to activate the atria and the AV node, but prevents the propagation of aberrant impulses from other anatomic sites in the atria. Severing may be accomplished, for example, by incising the full thickness of the myocardial tissue followed by closing the incision with sutures. The resultant scar permanently disrupts the conduction paths. As an alternative, permanent lesions, in which tissue is killed, can be created by ablation. The ablation process involves creating a lesion that extends from the top surface of the myocardium to the bottom surface (endocardial surface). Thus, the purpose of ablation is to create one or more lesions that sever certain paths for the excitations while keeping other paths intact. In the case of atrial fibrillation, for example, the lesions may interrupt the reentry circuit pathways while leaving other conduction pathways open. By altering the paths of conduction, the synchronization of the atrial contractions with the ventricular contractions may be restored. A plurality of lesions may be needed to achieve the desired results.
Incision through the myocardium, referred to as the xe2x80x9cmaze procedure,xe2x80x9d requires suturing to restore the integrity of the myocardium, and exposes the patient to considerable risk and morbidity. In contrast, thermal or other forms of ablation can create effective lesions without the need for sutures or other restorative procedures. Consequently, ablation can be performed more quickly and with far less morbidity. For these reasons, ablation is becoming a preferred method for severing conduction paths. The surgical ablation procedure may be performed during open-heart surgery. In a typical open-heart surgery, the patient is placed in the supine position. The surgeon must then obtain access to the patient""s heart. One procedure for obtaining access is the median stemotomy, in which the patient""s chest is incised and opened. Thereafter, the surgeon may employ a rib-spreader to spread the rib cage apart, and may incise the pericardial sac to obtain access to the cardiac muscle.
For some forms of open-heart surgery, the patient is placed on cardiopulmonary bypass (CPB) and the patient""s heart is arrested. CPB is preferred for many coronary procedures because the procedure is difficult to perform if the heart continues to beat. CPB, however, entails trauma to the patient with attendant side effects and risks.
In some circumstances, the patient may be treated by a procedure less invasive than the procedure described above. One such less invasive procedure may be a lateral thoracotomy. The heart may be accessed through a comparatively small opening in the chest and accessed through the ribs. In such a procedure, arrest of the patient""s heart may not be feasible, and if the heart cannot be arrested, the surgery must be performed while the heart continues to beat. Other procedures for access to the heart include sternotomy, thoracoscopy, transluminal, or combinations thereof.
Once the surgeon has obtained access to the heart, ablation can be carried out with a probe that delivers ablative energy. The ablative energy may take the form of electromagnetic radiation generated by a laser or radio frequency antenna. Other techniques for achieving ablation include the application of ultrasound energy or very low temperature. For the procedure to be successful, the created lesions should sever the targeted conduction paths. Typically, the surgeon must create a lesion of a particular length to create the desired severance. The surgeon must also create a lesion of a particular depth in order to prevent the electrical impulses from crossing the lesion. In particular, when the myocardial tissue is ablated, the lesion must be transmural, i.e., the tissue must be killed in the full thickness of the myocardium to prevent conduction across the ablation line.
The present invention is directed to surgical devices and methods useful in guiding surgical instruments during procedures on internal organs such as the heart. The device may take the form of a surgical xe2x80x9ctemplatexe2x80x9d device that is attached to the surface of an organ. The device can be configured to facilitate surgical procedures such as tissue ablation. For example, a surgical template can be used as a guide for travel of a surgical or ablative probe along a path to aid a surgeon in ablation of tissue to sever conduction paths in the heart and thereby alleviate arrhythmia. A surgical template device may be especially useful in operations where the organ tissue being treated is moving, e.g., for so-called beating heart surgery. The surgical template device may be effective in providing local stabilization of the tissue to which the tissue ablation procedure is directed. The devices and methods also may find use in procedures in which the pertinent organ is not moving.
Alternatively, the device may be configured to provide little or no stabilization, but provide guide structure for placement of the ablation probe in the same frame of motion as the moving tissue. In some cases, the template may incorporate hardware that structurally supports the instrument for travel along the ablation path. The template devices and methods can be configured for application of other types of therapeutic devices, such as diagnostic probes, pacing leads, and drug delivery devices, to the surface of a moving organ. To promote adhesion, in some embodiments, the device may be equipped with a compliant, tacky material that forms a seal for contact with tissue. The device also may be equipped with one or more vacuum ports that make use of vacuum pressure to enhance the attachment to the organ tissue. Adhesion refers to the ability of the device to hold fast to an organ on a temporary basis, either with the benefit of an adhesive or vacuum pressure or both. The present invention also is directed to surgical devices and methods useful in determining the effectiveness of a tissue ablation procedure. In some embodiments, a sensor may be integrated with a surgical template device as described above to assist the surgeon by making measurements that gauge whether the surgical procedure has been satisfactorily performed. For example, the surgical device may be configured to measure the effectiveness of an ablation procedure in terms of ablation length, depth or width. For example, the sensor may measure electrical characteristics of the tissue proximate the target conduction paths, e.g., tissue impedance, tissue conduction velocity, or tissue conduction time, as an indication of the effectiveness of the procedure. The information obtained by the sensor can be used as the basis for feedback to the surgeon, e.g., in audible and/or visible form. Moreover, the sensor information can be used as feedback for the closed-loop control of the tissue ablation probe. The sensor may be employed independently of a surgical template device.
As a further aid to the surgeon, the surgical template device may include indicators such as visible markings that show the targeted length of the ablation. The visible markings can be used as a reference by the surgeon during movement of the ablation probe within the template area provided by the device. Also, the template device may include a structure that physically restricts the length of travel of the ablation probe, as well as the shape of the path along which the probe travels. In particular, the length indicator may include a stop structure that extends into the path for travel of the ablation device and is oriented for abutment with the ablation device. In some embodiments, for example, the ablation template device may provide a linear path for travel of the ablation probe. In other embodiments, however, the template device may define a non-linear, e.g., curved, path for travel of the ablation probe.
Further, the present invention is directed to surgical devices and methods for manipulation of the heart and local stabilization of heart tissue for a tissue ablation procedure. In this aspect, the present invention may make use of a surgical template device that provides not only a guide for a tissue ablation procedure but also a structure that provides local stabilization of heart tissue within the operative area. In some embodiments, the ablation template device may be accompanied by a surgical manipulation device that adheres to the heart tissue and enables manipulation of the heart to provide the surgeon with a desired access orientation for the procedure. The manipulation device may permit lifting, pushing, pulling, or turning of the pertinent organ to provide the surgeon with better access to a desired area. For both the template and manipulation device, to promote adhesion, a compliant, tacky interface material can be provided for contact with tissue, along with one or more vacuum ports for use of vacuum pressure.
In addition to providing a guide for a procedure, a template device and associated methods can be arranged to provide structure that supports instruments such as ablation probes, diagnostic probes, pacing leads, and drug delivery devices, for application to the surface of a moving organ and active guidance along a path. For some surgical procedures, it is necessary to bring surgical instruments into contact with the surface of a particular organ. In addition to the ablation application described above, one example is the placement of one or more electrodes within or in contact with organ tissue to deliver electrical impulses to the organ tissue for various purposes, such as a pacing to control the beating of the heart. Another example is the placement of a syringe needle to deliver a medicament to a specific location on an organ. Although all these procedures could be performed manually by the surgeon when the body cavity is opened during surgery, each is made more difficult when performed via a small opening in the body cavity, usually through an endoscopy port. Moreover, such procedures are particularly complicated when the surface of the pertinent organ is moving, as with a beating heart.
Recently, some types of cardiac surgery have been performed through access ports or rather small incisions in the rib cage, instead of in the open field created by cutting through the sternum (a sternotomy) and spreading open the rib cage with a mechanical device. In these situations, there are occasions when surgical devices (diagnostic, therapeutic, etc.) will need to be affixed to a particular location on the heart surface without direct contact of the human hand. This might also be done while the heart is still beating. There is an increasing frequency of coronary artery bypass surgery done on beating hearts to avoid the morbidity associated with stopping the heart and placing the patient on cardiopulmonary bypass. Some surgeries on the beating heart are also performed using the traditional sternotomy. Access procedures such as sternotomy, thoracotomy, thoracoscopy, and percutaneous transluminal are contemplated.
To facilitate such procedures, a template device is provided to fix a particular surgical tool or diagnostic or therapeutic device within a defined operative path for the tool or device. There are some surgical procedures performed on a beating heart, or other organ, that will require the fixation of a surgical instrument, diagnostic device or therapeutic device to accomplish a specific surgical procedure, diagnostic measurement, or delivery of some therapeutic product or method. This is particularly true when such procedures, measurements, or deliveries are performed under minimally invasive conditions, such as through narrow tubes or ports that penetrate the skin and enter the abdominal or thoracic cavities. Template devices and associated methods, in accordance with the present invention, are useful in guiding surgical instruments, certain diagnostic sensors, or mechanisms for delivery of medicaments on the surface of internal organs, such as the heart.
The template devices and methods are particularly useful in attaching such instruments to the surface of the beating heart without any additional manual assistance of the surgeon, thereby facilitating certain procedures carried out both in open and minimally invasive procedures. Notable features of the template device include conformability to the contours of the organ, such as the heart, the ability to fix the device in place using vacuum, mechanical pressure, or adhesives, and atraumatic attachment by virtue of specific soft polymeric interfaces and shapes. The template device can be configured to attach to various surfaces of the heart using a vacuum seal. This device provides two or more vacuum ports surrounded by a conformable, compressible silicone gel or elastomer. As in the ablation template, these seals contain integrated electrodes for sending and receiving an electrical signal for the purpose of measuring impedance or conductance time or velocity across tissue in a treatment area. The electrodes may be surface or interstitial. Also, the electrodes may be multipolar, e.g., bipolar. In some embodiments, a single electrode within the seal may be sufficient with a reference electrode located elsewhere. A vacuum port or other fluid removal device may be desirable to remove fluids from the chamber to avoid the effects of such fluids on the electrical performance of the electrode(s) or electrical ablation devices. The ports can be attached to a single or multiple independent vacuum lines.
In some embodiments of the invention, ablation is performed on the interior surfaces of the tissues. For example, an ablating instrument may be directed transluminally, such as by way of a catheter, near the ostia of the pulmonary veins in the left atrium of the heart. Following the ablation and creation of a lesion, electrodes delivered by the catheter may be used to measure the efficacy of the ablation.
For radio frequency ablation, for example, enclosed in the body of the device can be a channel in which is located a moveable cable housing a radio frequency (RF) antenna for delivery of RF energy to the myocardium. The device allows the RF antenna to be moved by a remote control unit on the distal end of the cable. The cable can be moved through its channel by the controller in response to feedback from the sensors on the vacuum seals. As a lesion becomes transmural in one location, the sensors detect either decreases in impedance or increases in conduction time. This information is processed by the controller, and the RF antenna is moved by a motor that advances the cable assembly along a track in the device. Such a device is suitable for use in both open and minimally invasive procedures for the creation of linear transmural lesions for the treatment of atrial fibrillation.
Another embodiment is a similar device, which contains malleable metal elements that allow the device to be formed into an arc (like a shepherd""s crook) whose circumference can match the outer circumference of the base of the pulmonary vein. This device is similar in construction to the embodiment described above, except that it is attached to a rod suitable for insertion into a port access device for entry into the thorax or for manual manipulation by a surgeon in an open procedure. The device is brought into contact with the base of the pulmonary vein, and vacuum is used to attach it to a portion of the basal circumference of the vein. RF energy is delivered controllably as described above. When a full thickness lesion is created on one side of the vein, the vacuum is released, and the device moved so that its arc rests over the side of the vein that has not been treated. A full thickness lesion can then be created on that side.
For some applications, the surgeon may manually control advance of the radio frequency antenna within the template device, and control further movement with a remote control device. In particular, the surgeon can also utilize manual movement of the RF antenna assembly through a joystick or other actuation transducer that advances the RF antenna. The joystick is operated by the surgeon in response to an indicator (light, etc.) that responds to the appropriate decrease in impedance or increase in conductance time detected by the sensors mounted in the vacuum seals. As an alternative, the surgeon may simply monitor the advance of the radio frequency antenna visually, and actuate a joystick or similar device. In either case, the template device operates as both a guide and an automated actuator to translate the radio frequency antenna (or other device) along a desired path. Notably, the template device is affixed to the pertinent tissue and provides automated movement of the instrument, reducing motion problems relative to the instrument offering enhanced precision.
In one embodiment, the present invention provides a surgical device for use in a tissue ablation procedure. The device includes a contact member that engages the tissue near a location where the tissue is to be ablated. The contact member defines a guide that indicates, upon engagement of the contact member with the tissue, the location where the tissue is to be ablated, and provides a path for travel of a tissue ablation probe. The contact member of the device may include a compliant and tacky interface element for engagement with the tissue. The device may further define an interior chamber, and may include a vacuum port in fluid communication with the interior chamber. The interior chamber may be capable of delivering vacuum pressure to the contact member, thereby promoting vacuum-assisted adherence of the contact member to the tissue. In addition, the device may include a sensor that may indicate whether the desired degree of tissue ablation has been achieved.
In another embodiment, the present invention provides an apparatus for determining whether conduction paths within heart tissue have been adequately ablated during a surgical procedure. The apparatus includes a first electrode capable of transmitting a first electrical signal adjacent the tissue to be ablated, a second electrode capable of receiving a second electrical signal adjacent the tissue to be ablated and a measuring device electrically coupled to at least the second electrode to receive the second electrical signal from the second electrode. The measuring device may determine whether the extent to which the tissue has been ablated to a sufficient degree based on the second electrical signal. The apparatus further includes an output device that provides an indication of extent, e.g., depth, to which the tissue is ablated. In order to measure impedance when using RF ablation, it may be necessary to use an energy frequency outside of the ablation energy frequency range or pulse or ablation energy and measure impedance during the quiescent period between ablation pulses.
In another embodiment, the present invention provides a method for severing conduction paths within tissue. The method involves placing a first device near the target conduction paths to be severed, using the first device as a guide to sever the target conduction paths, and with a second device, measuring to determine whether the desired severing has been achieved. In this embodiment, the target conduction paths may be severed by tissue ablation. Measurement may involve determining whether the lesion depth is sufficient to sever the target conduction paths.